Method for reprogramming a field device

ABSTRACT

According to a method for reprogramming a field device, the current supply of the field device is increased in the programming mode. This enables electrically deletable and reprogrammable memories to be used in field devices.

[0001] The invention relates to a method for reprogramming a fielddevice.

[0002] In automation and process control technology, field devices areused in many ways that measure process variables in the process sequence(sensors) or that control controlled variables (actuators).

[0003] Field devices for determining flow, fill level, differentialpressure, temperature, etc. are widely known. For detecting thecorresponding process variables, that is, mass or volume flow, fillheight, pressure, temperature, etc., the field devices are disposed inthe immediate vicinity of the process component involved.

[0004] The field devices furnish a measurement signal which correspondsto the measured value of the process variable detected. This measurementsignal is carried to a central control unit (such as a control stationor process control system). As a rule, the process control is doneentirely from the control unit, where the measurement signals of variousfield devices are evaluated and as a function of the evaluation controlsignals for actuators that control the process sequence are generated.

[0005] As an example of an actuator, a controllable valve that regulatesthe flow of a liquid or gas in a pipeline segment can be named.

[0006] The signal transmission between the field device and the controlunit can be done in analog or digital form (for instance via a currentloop or a digital data bus).

[0007] Known international standards for signal transmission include forinstance 4- to 20-mA current loops, HART, PROFIBUS, FOUNDATION FIELDBUS,or CAN bus.

[0008] Along with analog field devices, programmable field devices arebeing increasingly used. Often, ASICs (application-specific integratedcircuits) and SMDs (surface mounted devices) are used for this purpose.

[0009] In the programmable field devices, more and more “intelligence”is thus shifted in the field to the actual site of use.

[0010] The applicable control program of the field device is stored in anonvolatile memory in the field device and is executed in amicroprocessor. This control program controls the operation, measurementand control functions, among others, of the field device.

[0011] In sensors that are used to detect measured values, normallylarger control programs are used than in actuators that are used foronly control purposes.

[0012] Because of the larger control programs, the versatility of thecontrol programs in sensors is greater.

[0013] Various functionalities are possible; for instance, the way inwhich data is stored can vary; the calibration can be done with variableprecision; data detection and data evaluation can differ; variousregulating and adjusting functions can be employed; the type of signaltransmission can differ; a more or less complicated self-monitoring(predictive maintenance) is possible, etc.

[0014] The field device, particularly as a sensor, no longer forwardsmerely a simple measurement signal but rather a prepared measurementsignal, optionally with further additional information. The total of allthese capabilities makes up the functionality of the field device.

[0015] For each functionality, a suitable control program (software) isrequired. The control program is normally stored in a nonvolatile memoryin the field device.

[0016] The functionality of a field device thus depends decisively onthe control program, which as a rule is made available by themanufacturer of the field device.

[0017] The control program can include certain basic functions orexpanded functionalities.

[0018] The control program is normally implemented upon manufacture ofthe field device; that is, after production the functionality of thefield device is fixedly specified and can no longer be altered in asimple way. In the event of program updates, or new functionalities(upgrades), replacement of the program is necessary.

[0019] One possibility is to replace the memory in which the controlprogram is stored. This replacement must be done by skilled workers andis complicated.

[0020] Another possibility is not to replace the memory but instead toreprogram it. This can be done for instance with the aid of a portableoperator control unit (such as a handheld computer or PC), whichconnected to the field device. Via a suitable interface in the fielddevice, the new control program is transferred from the operator controlunit to the field device and is stored in memory in the field device.

[0021] For some time, electrically erasable and reprogrammable memories,known as flash memories or flash EPROMS, that allow simple reprogramminghave been known.

[0022] However, one disadvantage of such memories is that thereprogramming requires a power supply that supplies strong current,which is above the normal basic current for field devices, and so thesespecial memories are not used in field devices.

[0023] The object of the invention is to disclose a method forreprogramming a field device with an electrically erasable andreprogrammable memory that is simple to perform.

[0024] This object is attained with the aid of the following methodsteps:

[0025] a) interruption of an ongoing first control program of themicroprocessor and switchover from a normal operating mode to aprogramming mode;

[0026] b) increasing the power supply to the field device;

[0027] c) erasing the first control program in the memory by applicationof a voltage;

[0028] d) storing a second control program in the memory;

[0029] e) cancelling the programming mode and starting the secondcontrol program.

[0030] Only by increasing the power supply in the field device isreprogramming of the memory possible.

[0031] In a preferred feature of the invention, during the programmingmode, a voltage pulse is generated at a control output of themicroprocessor.

[0032] In a preferred feature of the invention, the second controlprogram is read in via an interface provided in the field device.

[0033] The subject of the invention is also a field device that makes itpossible to perform the method of the invention.

[0034] Such a field device has an electrically erasable andreprogrammable memory and a regulatable power supply unit.

[0035] Because the power supply of the field device is adjustable, thepower supply of the field device can be increased above the basiccurrent demand during reprogramming, and the reprogramming of the memorycan thus be performed. In a preferred feature of the invention, thefield device has a field bus interface as a connection to a digital databus, and this interface serves as the power supply unit.

[0036] In a preferred feature of the invention, the field bus interfacehas a control input, whose resistance at the voltage zero pointregulates the power supply of the field device.

[0037] In a preferred feature of the invention, the control input isconnected to ground via two series-connected resistors, and the secondresistor can be bridged by means of a transistor.

[0038] The invention is explained in further detail below in terms of apreferred exemplary embodiment shown in the drawings. Shown are:

[0039]FIG. 1, a schematic illustration of a data bus system with aplurality of field devices;

[0040]FIG. 2, a schematic illustration of a field device.

[0041] In FIG. 1, a data bus system DBS with a plurality of fielddevices and with a process control system PLS is shown. The fielddevices involve sensors S and actuators A. The data bus participantscommunicate with one another via a data bus line DBL.

[0042] The process control system PLS is as a rule disposed in a controlroom, from which all the process control is done centrally. The sensorsS and actuators A are disposed “in the field” in the various processcomponents (tank, filling apparatus, pipeline, etc.).

[0043] The sensors S1, S2 and S3 detect the process variables oftemperature T, pressure D and flow F, for instance, each at a particularprocess component. The actuators A1 and A2 are for instance valvecontrols that regulate the flow of a liquid or gas through a pipelinesegment.

[0044] The data communication between the process control system PLS andthe sensors S and actuators A is effected in a known manner inaccordance with an internationally standardized transmission technique(such as RS 485 or IEC 1158), using special protocols (such as PROFIBUSor FOUNDATION FIELDBUS, CAN bus).

[0045] In FIG. 2, the sensor S1 is shown in further detail as an exampleof a field device. The sensor S1 is connected directly to the data busline DBS. The connection is made by means of a T coupler T, whichconnected to a field bus interface FBS via a data line DL1. The fieldbus interface FBS supports all the transmission and reception functionsfor the transmission technique employed.

[0046] From the field bus interface FBS, a data line DL2 leads to acommunications unit KE, which reads telegrams from the data bus line oritself writes telegrams to the data bus line DBL.

[0047] The communications unit KE communicates with a microprocessor μpvia a data line DL3. The control program of the microprocessor μp isstored in a nonvolatile memory EE. The memory EE is a so-calledelectrically erasable and reprogrammable memory (flash memory or flashEPROM). The microprocessor μp is also connected to an interface S, whichserves as a connection for an external memory unit, such as a portablepersonal computer. Via this interface S, control programs and data fromexternal memories can be transmitted to the field device.

[0048] The microprocessor μp is also connected to a measured valuepickup MWA via an A/D converter AD. The A/D converter converts theanalog measurement signal of the measured value pickup MWA into adigital measured signal that is processed in the microprocessor μp.

[0049] From a control output A1 of the microprocessor μp, a control lineSL leads to the base terminal B of a transistor T, whose emitterterminal E leads to a voltage divider, constructed of two resistors R1,R2, that is connected to one control input E1 of the field bus interfaceFSB.

[0050] The field bus interface furnishes the entire power supply of thesensor S1.

[0051] According to the invention, the power supply level of the sensorS1 can be adjusted by means of the resistance between the control inputE1 and the ground zero point.

[0052] This value is defined via the two resistors R1 and R2.

[0053] The method of the invention for reprogramming a field device isdescribed in further detail below.

[0054] In a first method step, the ongoing control program of themicroprocessor μp is interrupted, and the microprocessor μp switchesover from a normal operating mode to a programming mode.

[0055] In a second method step, the power supply of the field device isincreased;

[0056] in a third method step, the old control program in the memory EEis erased by application of a voltage;

[0057] in a fourth method step, the memory EE is written with a newcontrol program;

[0058] in a fifth method step, the programming mode is cancelled, andthe new control program is started.

[0059] Only by increasing the current can the memory EE be reprogrammed.

[0060] In a preferred feature of the method of the invention, during theprogramming mode, a voltage pulse is generated at a control output S1 ofthe microprocessor μp. With this voltage pulse, the power supply can becontrolled. As long as the voltage pulse is applied, the field devicerequires more current.

[0061] The new control program is read in via the interface S. Aportable operator control unit such as a PC (personal computer) or“handheld” can simply be connected to this interface S. The new controlprogram is stored in a memory of this operator control unit and istransferred in a known manner.

[0062] The method of the invention can be employed only with a fielddevice S1 that has an electrically erasable and reprogrammable memoryEE. In addition, a regulatable power supply unit is needed. Regulatablepower supply units are available commercially.

[0063] A regulatable power supply unit os this kind is provided by thefield bus interface FBS.

[0064] The essential concept of the invention is to disclose a methodand a device with which simple reprogramming of a field device ispossible.

1. A method for reprogramming a field device, which has a microprocessorμp and an electrically erasable and reprogrammable memory EE, having thefollowing method steps: a) interruption of an ongoing first controlprogram of the microprocessor μp and switchover from a normal operatingmode to a programming mode; b) increasing the power supply to the fielddevice; c) erasing the first control program in the memory EE byapplication of a voltage; d) storing a second control program in thememory EE; e) cancelling the programming mode and starting the secondcontrol program.
 2. The method of claim 1, wherein during theprogramming mode, a voltage pulse is generated at a control output A1 ofthe microprocessor μp.
 3. The method of one of the foregoing claims,wherein the second control program is read in via an interface Sprovided in the field device.
 4. A field device for detecting orcontrolling a process variable, which has a microprocessor and a memoryin which a control program is stored that determines the function of thefield device and which has a power supply unit, characterized in thatthe memory EE is electrically erasable and reprogrammable, and the powersupply unit is regulatable.
 5. The field device of claim 4,characterized in that serving as the power supply unit is a field businterface FBS, which is connected to a digital data bus DBS.
 6. Thefield device of claim 4 or claim 5, characterized in that the field businterface FBS has a control input E1, whose resistance at the voltagezero point regulates the power supply of the field device.
 7. The fielddevice of claim 6, characterized in that the control input E1 isconnected to ground via two series-connected resistors R1, R2, and thesecond resistor R2 can be bridged by means of a transistor T.